Abstract

Silicified polyplacophoran faunas from the Permian of West Texas in the U. S. National Museum and American Museum of Natural History collections comprise the largest known Permian collection. A total of 543 specimens, as individual plates, are present and among which 472 (87%) represent one species, Pterochiton arthurcooperi and 7 (1.3%) P. newelli, both described by Smith (1976). The remaining specimens are represented by Helminthochiton girtyi n. sp., the new genera and species Ochmazochiton comptus, Chauliochiton knighti, Stegochiton coxi, S.? onerosus, Soleachiton yochelsoni, Lekiskochiton fornicis and three indeterminate genera and species. The stratigraphic range of the family Acutichitonidae Hoare, Mapes and Atwater is confirmed as extending at least from the Lower Carboniferous to the Permian and is emended to contain taxa having primitively slitted insertion plates, as well as the development of a hypotyche. The genus Helminthochiton is described from the Permian for the first time, extending its range above the previously known Lower Ordovician to Middle Pennsylvanian occurrences. Specimens of Pterochiton arthurcooperi Smith from the Bone Spring Formation have preserved color patterns of longitudinally positioned, V-shaped light bands on a darker background.--Modified journal abstract.

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